Embodiments of the invention relate generally to the field of medical diagnostics and more specifically encompass methods and devices for producing a white blood cell (WBC) count without the need for lysing the red blood cells (RBCs) and without the need for coincidence correction.
A common medical test that is used for the determination of a patient's health is the complete blood count (CBC) which determines the number of various types of blood cells per unit volume of the patient's blood. One type of blood cell that is counted is the white blood cell.
White blood cells, known also as leukocytes, are cells released by the immune system to fight infection and respond to foreign matter in the body. There are many types of white blood cells, including neutrophils; eosinophils; basophils; lymphocytes and monocytes. These cells are generally named according to the types of stains that they absorb.
In a healthy adult, white blood cells make up about 1% of the blood cells which corresponds to 4×103 to 1×104 cells per microliter of blood. Deviations from this range may indicate a disease state. Some diseases, such as leukemia or infections, result in leukocytosis, a rising of the white blood cell count. Some diseases result in leucopenia a lowering of the white blood cell count. These diseases include viral infections or bone marrow disorders.
Another blood cell type is the reticulocyte. A reticulocyte is an immature red blood cell. Reticulocytes include a reticulum of ribonucleic acid (RNA) which is lost as the cells mature into red blood cells. Typically reticulocytes are 0.5%-1.5% of the red blood cells in the adult body. The number of reticulocytes may increase as a result of blood loss, for example in injury, or red blood cell destruction, for example, in certain types of anemia. Low reticulocyte counts may be the result of other types of anemia, exposure to radiation, or certain medicines which affect the bone marrow.
Exemplary present day hematological analyzers utilize flow cells to count and characterize blood samples. These devices include a number of specimen processing modules which are programs used to selectively identify the blood cells in the sample. For example a reticulocyte module permits red blood cells and reticulocytes to be counted.
However, a problem in obtaining an accurate WBC count can occur when the patient's white blood cell count is significantly elevated. In these cases the impedance based WBC count module that the hematological analyzer typically uses has trouble directly distinguishing individual white blood cells because of coincidence. Coincidence issues arise when the concentration of a cell type is high enough that the analyzer cannot distinguish the individual cells and counts two or more cells as one. Coincidence correction affects all WBC counts but with higher impact for increased concentrations of WBCs. Without correction the result is that the white blood cell concentration may be underreported. Existing approaches attempt to correct for these issues algorithmically to adjust for coincidence.
Hence, although WBC count systems and methods are currently available and provide real benefits to patients in need thereof, many advances may still be made to provide improved devices and methods for assessing the status of WBCs in an individual. Embodiments of the present invention provide solutions that address these problems, and hence provide answers to at least some of these outstanding needs.